II.   Delta-Thalassemia Alleles

A total of 17 different delta-thal alleles have been reported; most result in the absence of any delta chain synthesis but some should be considered delta+-thal variants. Their presence has no clinical consequences; however, when such a delta-globin gene mutant is observed, either in cis or in trans to a beta-thal allele, complications in the diagnosis of the beta-thal heterogeneity may occur because of a normal Hb A2 level of 2.0-2.5%. The 17 alleles are described in detail on pages 174 through 184; they are listed from 5' to 3' according to the locations of the changes. The sequence of the delta-globin gene is given in Fig. 8. The delta-thal alleles can also be listed according to the functional changes caused by the mutation or deletion as is shown in Table XVI.

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FIG. 8. Sequence-Reading Chart for the Delta-Globin Gene

This material is from the book A Syllabus of Thalassemia Mutations (1997) by Titus H.J. Huisman, Marianne F.H. Carver, and Erol Baysal, published by The Sickle Cell Anemia Foundation in Augusta, GA, USA. Copyright © 1997 by Titus H.J. Huisman. All rights reserved. Neither this work nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, microfilming and recording, or by any information storage and retrieval systems, without permission in writing from the Author.